Hello,

I've researched this problem a bit. It doesn't look like povray can do things
the way I hoped it would.

Basically I want to generate a "cut away" of a complex assembly. I routinely use
povray as a modeling tool to render mechanical designs before I fabricate them.
As one might imagine generating a cut-away of the design is quite useful.

The logical choice here would be to use the "difference" command. The problem
is that although it is *claimed* that objects are assumed to be solid, in
reality it seems "difference" puts a *cap* on the (hollow) object its
differencing. Evidence of this can be seen when using the pigment "Clear" on
the object being differenced.

ie.,

difference
  {
  cylinder
    {
    <0.0, 0.0, 1.0>
    <0.0, 0.0,-1.0>
    1.0
    pigment{Yellow}
    }

  box
    {
    <0.0, 2.0, 2.0>
    <2.0,-2.0,-2.0>
    pigment{Clear}
    }
  }

()Produces a hollow cylinder cut in half.

The idea that after something is *subtracted* from another thing, leaves
something of itself behind in the result
(ie., 7-3 = 4 + (bits of "3" sprinkled on it) doesn't seem consistent with the
idea of a *difference* to me.

Anyway, the only answer I can see is to live with a *single* pigment bounding
the cutaway regions (unfortunate since I'd loose all the pigments of the various
sub-components) or meticulously cut away each sub-component separately to
produce a combined cut-away object with the pigments of the various
sub-components preserved.

Suggestions appreciated.

Thanks.

Robert W.

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